Water, for irrigation and other purposes, is often carried by a system of ditches and the inner surfaces of these ditches are often lined with concrete or other suitable paving material. In some instances, movement or flow of the water is induced and controlled by pumps and valves or gates and in other instances, it is highly desirable to induce and control the movement or flow of the water by means of the slope or fall of the ditches in the system. In these latter instances, it is essential that the slope, grade, or fall of the ditches be accurately controlled to very close tolerances. For example, the specification of one installation required a slope of 30 cm. per 200 meters with a tolerance of plus or minus 1 cm.
Heretofore, attempts to accurately control the slope or fall of such ditches have essentially involved digging such ditches with a slope as close to the desired slope as possible and then to line the ditches with a liner of uniform thickness. As can be readily appreciated, it is virtually impossible to dig any ditch with powered digging machines to any reasonably close tolerances and hand labor is very time-consuming and costly. Further, even with hand labor very close tolerances in the slope or fall of the bottom of the ditch being dug is very difficult to achieve.
Another prior attempt has involved building forms along the ditch and filling the forms with concrete. Then, the forms are removed when the concrete is partially set. The building and removal of the forms are costly and time-consuming operations and also present problems in the finishing of certain surfaces of the concrete within the ditch.
Several different types of devices have been proposed for forming concrete linings in ditches and the like. However, the slope or fall of the bottom of the lining has been dependent upon the slope imparted to the ditch when it is being dug. Therefore, such devices suffer from the same deficiencies as discussed above.